U.S. Pat. No. 5,805,061 (Fritz et al.) discloses an electronic flasher unit 10 for a vehicle lighting system. The flasher unit 10 includes an integrated control circuit 16 for operating blinker lamps 19. The circuit 16 has an open-loop control input 6 and a relay driver output 1. Additional terminals 2, 3, 4, 5, 7 and 8 of the control circuit 16 will be described in more detail below. The control input 6 of the integrated circuit 16 is connected through a resistor R.sub.4 to a hazard input terminal 13 which in turn is connected to a warn-blinker switch 20 that is manually operable. The relay driver output 1 is connected to one terminal of a relay 17 and provides a control signal for energizing the relay 17 to operate relay contacts 17' and 17". The other terminal of the relay 17 is connected through a terminal 15 with a reference potential such as ground. The operational mode "warn-blinking" is established when the switch 20 is closed. The relay contact 17' establishes a power supply circuit for two warn-blinking lamps 19 as follows: battery 23, terminal 14, shunt resistor R.sub.3, relay contact 17' closed, terminal 13, warn-blinker switch 20, warn-blinking lamps 19, ground. A further power supply circuit is established through the relay contact 17" for one or the other blinker lamp 19' for right and left blinking depending on the position of the manually operable directional blinker switch 21.
When the warn-blinker switch 20 is closed, ground potential is temporarily applied to the control input 6 of the circuit 16 through the resistor R.sub.4, the warn-blinker switch 20, and the warn-blinking lamps 19, whereby the integrated circuit 16 is switched into the operational mode "warn-blinking" and the relay 17 is energized. As soon as the relay 17 has closed its contact 17', the battery voltage is connected to the control input 6, through the terminal 14, the shunt resistor R.sub.3, the contact 17', and the resistor R.sub.4, whereby the operational mode "warn-blinking" is switched off. Since, however, the warn-blinker switch 20 remains closed, the operation mode "warn-blinking" is switched on again when the relay contact 17' is opened so that the integrated circuit 16 can assume an oscillating operational mode.
In order to prevent this oscillating operational mode, it is necessary that a signal holding circuit in the integrated circuit makes sure that the ground potential that has been connected to the control input 6 by the closing of the warn-blinker switch 20 is maintained as long as the warn-blinker switch 20 is closed.
German Patent Publication DE 4,113,455 C2 discloses an analog circuit arrangement having the required holding function, however, with the disadvantage that in the operational mode "warn-blinking" additional circuit components are required for maintaining the low level, namely a resistor R.sub.8 integrated into the circuit IC, a second external shunt resistor R.sub.7 and a comparator K.sub.1. Since the comparator K.sub.1 must be maintained in its active state even if the engine ignition is switched off in order to switch on the operational mode "warn-blinking" a quiescent current of typically 100 .mu.A keeps flowing, which is undesirable for battery power preservation.